1. Necessity
Determination of engine condition. By measuring CO/HC, it is possible to determine the engine condition, including the effectiveness of the airfuel ratio, and the operation of the emission control system. It can be determined that the engine and emission control system are normal when the CO and HC are within the standard value, and the engine operates smoothly. When the engine does not operate smoothly or HC levels are high, engine misfire is a probable cause. Causes of engine misfire are improper air-fuel ratio, poor compression, ignition system trouble, or emission control system trouble, etc. For meeting regulations.
2. With TWC/oxygen sensor
It is not necessary to adjust the CO level because the engine control system increases and decreases the fuel injection volume coming out of the injector to adjust the air-fuel ratio to more closely match the theoretical air-fuel ratio, using the oxygen sensor signal.
Most of CO and HC are purified by the TWC even if some misfiring occurs.
When CO and HC are detected, the following are probable causes: Poor or insufficient warm-up of TWC, rich air-fuel mixture, a high rate of misfire.
3. Without TWC/oxygen sensor
It is necessary to adjust the CO level within the standard value in order to meet the regulations and use the engine in good condition.
The air-fuel mixture is rich when CO/HC concentration is high and the engine runs smoothly. It is necessary to adjust the CO concentration in order to keep emission gases clean, even though the engine operates more smoothly when the CO concentration is higher than the standard value.
When the CO concentration is too low, the HC concentration is high and the engine does not operate smoothly, causing misfires to occur.